1. Field of the Invention
This invention relates to a dry-spun fiber made from a polyether-based spandex polymer which was formed by reacting a poly(tetramethylene ether) glycol with methylene-bis(4-phenylisocyanate) and then chain extending the resultant isocyanate-capped product with a mixture of ethylene diamine and a minor amount of a second diamine. In particular, the invention concerns an improvement in such a fiber, wherein the second diamine of the diamine mixture is 2-methyl-1,5-pentanediamine in a very narrow concentration range. The improved spandex fiber is particularly suited for use in tricot-knit fabrics.
2. Description of the Prior Art
Polyether-based spandex fibers derived from a poly(tetramethylene ether) glycol that was capped with methylene-bis(4-phenyl-isocyanate) and then chain extended with a diamine mixture that included ethylene diamine are known. Such a polyether-based spandex fiber is sold by E. I. du Pont de Nemours and Company as Type-136 Lycra.RTM. spandex yarn. These commercial yarns, which are made from a spandex polymer that had been was chain extended with an 80/20 molar mixture of ethylene diamine and hydrogenated m-phenylenediamire (also known as 1,3-diaminocyclohexane), have a highly satisfactory combination of tensile and elastic properties. However, tricot-knit nylon fabrics that include a minor percentage of the commercial spandex yarns in their construction often exhibit undesirable curling at the edges after being heated during finishing (e.g., in heat-setting or dyeing steps). Improvements are needed in the polyether-based spandex yarns to enhance the utility in knit fabrics.
The use of mixtures of diamines for the chain extension step in the preparation of various types of spandex polymers is also known in the art from published United States patents. Among others, Frazer et al U.S. Pat. No. 2,929,803, Wittbecker U.S. Pat. No. 3,507,834 and McMillin et al U.S. Pat. No. 3,549,596, each disclose that mixture of chain extenders may be employed in making spandex fibers. For example, in column 9, lines 55-74, Frazer et al lists primary and secondary diamines that may be mixed for use in the chain-extension step. However, the art does not disclose the use of 2-methyl-1,5-pentanediamine as a chain extender for making spandex polymer. Nor does the art disclose the use of 2-methyl-1,5-pentanediamine with ethylene diamine in the very narrow concentration ranges required in accordance with the present invention.
A purpose of this invention is to provide an improved spandex fiber that retains the favorable balance of tensile and elastic properties of commercial polyether-based spandex fiber, but improves the performance of spandex fiber in knit fabrics that are intended to be heat set.